The manufacture of thin film capacitors is well known. One method for the manufacture of thin film capacitors is to first form a thin film of a metal, such as tantalum, as the first electrode on a dielectric substrate. This composite is then placed in an anodizing bath to form a dielectric layer of tantalum oxide on the tantalum film. This procedure requires a lengthy period of time, thereby adding greatly to the cost of manufacturing a capacitor. Furthermore, the tantalum oxide formed on the tantalum film by the anodizing technique is deficient in oxygen and a relatively thick coating of the tantalum oxide is required to provide acceptable capacitance parameters.
U.S. Pat. No. 4,002,545 to Fehiner et al. describes an improved method of forming a thin film capacitor having a tantalum oxide dielectric. In the method of the Fehiner et al. patent, a non-tantalum electrically conductive film is applied to a dielectric substrate to form a first capacitor electrode. A thin film of tantalum is then applied over the electrode to form an electrically conductive duplex film. The substrate with the applied duplex film is then placed within a vacuum environment containing a mixture of oxygen and an inert gas. A film of tantalum oxide is R-F sputtered over the duplex film within the vacuum environment. The dielectric substrate and duplex film with the tantalum oxide film applied thereon is then cooled and an electrically conductive film is applied over the film of tantalum oxide to form a counter capacitor electrode.
It is indicated in the Fehiner et al. patent that the method of the patent cures the problem of oxygen deficiency which is encountered during R-F sputtering of a tantalum oxide film onto a tantalum substrate. A basic disadvantage of the method of the Fehiner et al. patent and other known methods for making thin film capacitors is that these methods cannot produce a dielectric thickness of less than about 2,000 A which have suitable characteristics in respect to temperature coefficient of capacitance, leakage and loss, particularly at temperatures above 200.degree. C. The requirement for ultra-thin dielectric film has been accentuated recently due to the desire for increased packing densities. A requirement has been set for thin film capacitors having a dielectric constant (.epsilon.) to thickness (expressed in Angstrom units) ratio of greater than about 0.04. Since most metal oxides suitable for use as a dielectric have a dielectric constant of from about 15 to about 60, a thickness of less than about 1,500 A must be established to meet the .epsilon./t requirement of greater than 0.04.
Accordingly, it is an object of this invention to provide an ultra-thin film capacitor of less than about 1500 A and a method of production of ultra-thin film capacitors which will have desired characteristics of capacitance, temperature coefficient of capacitance, leakage and loss.